1. Field of the Invention
The invention relates to a method for adhesive bonding of surfaces with a foam comprising a foamable mixture containing alkoxysilane-functional prepolymers.
The invention relates to a method for adhesive bonding of surfaces with a foam comprising a foamable mixture containing alkoxysilane-functional prepolymers, and to a foamable mixture.
2. Description of the Related Art
Prepolymer systems which have reactive alkoxysilyl groups have long been known and are often used for production of resilient sealants and adhesives in industry and the construction sector. In the presence of atmospheric moisture and suitable catalysts, these alkoxysilane-terminated prepolymers are capable, at as low as room temperature, of condensing with one another with elimination of alkoxy groups and formation of an Si—O—Si bond. Thus, these prepolymers can be used, inter alia, as one-component systems which have the advantage of simple handling since no second component has to be metered in and admixed.
A further advantage of alkoxysilane-functional prepolymers consists in the fact that neither acids nor oximes or amines are liberated on curing. Moreover, in contrast to isocyanate-based adhesives or sealants, there is no formation of gaseous CO2, formation of which would subsequently expand the adhesive material after adhesive bonding of components. Furthermore, alkoxysilane-functional prepolymer mixtures are toxicologically safe, in contrast to isocyanate-based systems.
A particularly advantageous type of alkoxysilane-functional prepolymers comprises alkoxysilane-terminated prepolymers. These may be composed of different building blocks. Usually, these prepolymers have an organic backbone, i.e. they are composed, for example, of polyurethanes, polyethers, polyesters, polyacrylates, polyvinyl esters, ethylene-olefin copolymers, styrene-butadiene copolymers or poly-olefins, described, inter alia, in EP 0 372 561, WO 00/37533 or U.S. Pat. No. 6,207,766. However, systems whose backbone consists completely or at least partly of organosiloxanes are also widely used, described, inter alia, in WO 96/34030.
In a particularly advantageous preparation process for alkoxysilane-terminated prepolymers, starting materials used are polyols, for example polyether polyols or polyester polyols, which are reacted in a first reaction step with an excess of a di- or polyisocyanate. Thereafter, the isocyanate-terminated prepolymers obtained thereby are reacted with aminoalkyl-functional alkoxysilanes to give the desired alkoxysilane-terminated prepolymer. Alternatively, it is also possible to prepare alkoxysilane-terminated prepolymers by reacting a polyol or an OH-functional polyurethane, as can be prepared by the reaction of polyols with less than the stoichiometric amount of di- or polyisocyanates, with an isocyanatoalkyl-functional alkoxysilane. These preparation processes are described, for example, in EP 1 421 129 or WO 2005/000931. Further preparation processes, for example the reaction of aminofunctional polyols with carbamatoalkylalkoxysilanes, described in WO 02/34838, are also conceivable.
Furthermore, alkoxysilane-functional prepolymers having a poly(meth)acrylate backbone are also known. These are typically synthesized by copolymerization of (meth) acryloyloxyalkylalkoxysilanes with other (meth)acryloyl monomers and/or further unsaturated monomer building blocks, such as, for example, styrene.
In addition, alkoxysilane-functional polymers can also be prepared by subsequent grafting on of unsaturated alkoxysilanes, for example of vinyl- or (meth)acryloylsilanes.
In addition to a use as adhesive, use of alkoxysilane-functional prepolymers for the preparation of silane-crosslinking rigid and flexible foams, in particular of isocyanate-free sprayable construction foams, is also known and is described, for example, in EP 1 098 920 B1 or EP 1 363 960 B1. These spray foams are typically applied from spray cans and serve in particular for sealing of window joints, as filling and fixing material for door frames or generally for filling and sealing cavities in a structure. According to these applications, they are distinguished by as low a foam density as possible, i.e. as great a volume yield as possible per foam can and hence as high a productivity as possible. The low foam densities are achieved by application of as large an amount as possible of physical blowing agents, i.e. gas which is liquefied under pressure in the foam can and drives the foam formation during the spray process.
Such spray foams are unsuitable for use in conventional adhesive bonding applications in particular because they initially do not have any significant initial mechanical strength after their foaming and the workpieces to be adhesively bonded accordingly would have to be fixed over extremely long periods.